1. Field of the Invention
The present invention relates to electrical contacts, more particularly, to methods of manufacturing crimp ears.
2. Description of the Related Art
It is well known in the prior art to manufacture electrical contacts by stamping and forming from a continuous strip or ribbon of metallic, conductive material. During the stamping or punching operation, the ribbon is fed into a progressive stamping die that punches profiles of the flat terminals, which are then formed into the desired three-dimensional shape.
The typical electrical contact has a contact portion and a rounded crimp ear for attaching a wire. The inner surface of the crimp ear is typically stamped with narrow grooves or serrations to provide a more secure wire attachment. For some contacts, particularly small contacts, the developed length, that is, the length of the flattened crimp ear, will be greater than the corresponding dimension of the contact end. There are two general methods of forming a crimp ear of this type. In the conventional formed ear method, the ribbon is punched with the ear at its developed length. Features such as coins and serrations are added and the ear is formed to the proper configuration. With this method, ears can be formed with consistent parameters. However, because the developed length is wider than the contact portion, there is wasted material between the contacts. And because the ear is only a small portion of the total length of the contact, on the order of 10–20%, the amount of waste can be significant.
The second method of forming a crimp ear begins by punching an ear no greater than the width of the contact so there is a minimal waste of material between contacts. The ear forming sequence utilizes a swaging operation to achieve the developed length necessary to form the ear. In the five-stage swaging operation shown in FIG. 2, the dies lengthen the ends of the ear by thinning the ear material. In the first stage, the ends of the ear 50 are sheared from the strip 52, as at 54. In the second stage, the ear 50 is preformed by bending it at the longitudinal centerline 56 of the contact. Stage 3 begins the swage formation by pushing material to the ends, as at 58. Stage 4 completes the swage formation by stretching out the ends, as at 60. Stage 5 completes the formation by bending the ear ends to the appropriate angle 62.
Although there is considerably less waste than with the conventional formed ear of the first method described above, the quality of a swaged ear is substandard. Swaging is a severe method of forming. Besides generating excessive friction and tool wear, other process variables, such as variance in lubrication and stamping material properties can have a dramatic effect on the quality of the swaged ear. It has been documented throughout the years that the swaging operation is a costly, labor-intensive forming method in terms of its use in progressive dies. Dimensional tolerances must be liberal when swaging is used.
Additionally, the serrations cannot extend across the developed length of the ear because (1) the swaging operation causes any serrations to distort to the point where they essentially disappear and (2) because the thinner material at the serrations can become weak points in the ear after swaging. Consequently, as shown in FIG. 3, the serrations 64 are restricted to the center of the ear where the material is not stretched during the swaging operation.